1. Field of the Invention
This invention relates to an electrophotographic image forming apparatus, and more particularly to a developer housing for compact single component development systems with modified toner agitator and a shrouded dispense auger disposed inside a holey tube for use in color reprographic systems.
2. Description of Related Art
In general, an electrophotographic printing machine requires a photoconductive member that is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is thereafter exposed to a light image of an original document to be reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. Alternatively, in a printing application, the electrostatic latent image may be created electronically by exposure of the charged photoconductive layer by an electronically controlled laser beam. After recording the electrostatic latent image on the photoconductive member, the latent image is developed by bringing a developer material charged of opposite polarity into contact therewith. In such processes, the developer material may comprise a mixture of carrier particles and toner particles or toner particles alone. Toner particles are attracted to the electrostatic latent image to form a toner powder image which is subsequently transferred to a copy sheet and thereafter permanently affixed to the copy sheet by fusing.
In the foregoing type of printing machine, a development system is employed to deposit developer material onto the electrostatic latent image recorded on the photoconductive surface. Generally, the developer material comprises toner particles adhering triboelectrically to coarser carrier granules. Typically, the toner particles are made from a thermoplastic material while the carrier granules are made from a ferromagnetic material.
Alternatively, a single component magnetic material may be employed. A system utilizing a single component developer material, such as disclosed herein, is capable of high speeds, thus, a single component developer system readily lends itself to applications involving high speed electrophotographic printing machines. However, a large continuous supply of toner particles must be available to be capable of copying large numbers of original documents or producing multiple copies of the same original document. This is necessary to insure that the machine is not shut down at relatively short intervals due to the lack of toner particles. Ideally, this is achieved by utilizing a remote toner sump containing a large supply of toner particles positioned remotely from the developer housing in the printing machine. The toner particles are then transported from the toner sump to the development system.
Notably, it has been found that it is frequently difficult to locate the toner sump within the printing machine while still optimizing the printing machine architecture. This is due to the need for multiple color housings and the fact that the toner particles do not readily move against the gravitational force. Hence the toner sump is typically positioned above the development system. Under these circumstances, this restricts the machine architecture. Further, it is highly desirable to be capable of developing a latent image with insulating, non-magnetic toner particles. Insulating toner particles (i.e., for color reprographics) optimize copy quality, however, the problem of transporting these toner particles from a remote location must be overcome.
Further, since toner material is consumed in a development process and must be periodically replaced within a development system to sustain continuous operation of the machine, various techniques have been used in the past to replenish such toner supply. Initially, new toner material was added directly from supply bottles or containers by pouring into the dispensing apparatus fixed in the body of the reprographic machine. The addition of such gross amounts of toner material altered the triboelectric relationship between the toner and the carrier in the developer resulting in reduced charging efficiency of the individual toner particles and accordingly in reduction of the development efficiency when developing the latent image on the image bearing surface. In addition, the pouring process was both wasteful and dirty in that some of the toner particles became airborne and would tend to migrate into the surrounding area and other parts of the machine.
Accordingly, separate toner or developer hoppers with a dispensing mechanism for adding the toner from the hopper to the developer apparatus in the automatic machines on a regular or as needed basis have been provided. In addition, it is a common practice to provide replenishing toner supplies in a sealed container which, when placed in the printing machine, can be automatically opened to dispense toner. In such systems, the developer may be dispensed from the container relatively uniformly, although difficulty may arise in uniformly dispensing the developer since a large mass of toner particles (which frequently are somewhat tacky) may tend to agglomerate (i.e., become compacted) and form a bridging structure in the toner container.
Additionally, with the use of removable or replaceable developer cartridges, and due to the relative high cost of the developer contained therein, it is desirable to remove as much of the developer as possible during the dispensing operation from the cartridge so that only a minimal quantity of developer is not dispensed for use in the formation of images. Excessive quantities of developer undispensed and remaining in an empty developer cartridge increase the cost per copy to the consumer.
For electrophotographic purposes, composite development systems are known. For instance, U.S. Pat. No. 4,926,217 to Bares, discloses an apparatus for moving toner particles from one end of a duct to the other end with means provided to fluidize the particles in the duct and means to generate a pressure differential to move the fluidized particles in the duct from one end to the other.
U.S. Pat. No. 5,187,524 to Cherian, discloses a helical spring auger for transporting developer from a toner dispenser cartridge to an entrance to the developer housing, or from a cleaning station adjacent the photoreceptor to a waste bottle.
U.S. Pat. No. 5,189,475 to Fournia et al., discloses a toner concentration sensor that is located adjacent a transport auger within the developer sump for use with a two component development system.
While the above described developer mechanisms provide for movement of toner particles in a transporting conduit, the do not do so in a fully effective manner.